The present invention relates to a corneal-shape measuring apparatus for measuring the shape of a cornea of an eye to be examined.
As an apparatus for measuring a corneal shape, a corneal topography apparatus for measuring the corneal curvature at a multiplicity of regions of the cornea and displaying its distribution as topography is known. In this apparatus, a measurement index of a predetermined pattern, such as a Placido ring, is projected onto the cornea of the eye to be examined, and its reflected image of the cornea (Placido ring image or the like) is photographed by a CCD camera or the like. Then, by subjecting the photographed image to image analysis, the curvature distribution in a substantially entire region of the cornea is determined, and is graphically displayed on a display.
However, in the image of the anterior eye segment including the cornea onto which the measurement index (Placido ring) has been projected, there is a difference in luminance (the quantity of light; hereinafter the same) between a pupil portion and an iris portion, so that it is difficult to discern the change of luminance in the image of the measurement index in the vicinity of a boundary between the pupil and the iris. Namely, as can be seen from a graph shown in FIG. 4 indicating the change of luminance on a straight line passing the center of the Placido ring image, since the iris region is photographed such that the luminance of the light reflected by the iris is added to the change of luminance of the Placido ring image, it is difficult to detect the edge of the Placido ring image. Hence, the measurement accuracy is lowered.
As an corneal-shape measuring apparatus incorporating an objective occular-refractive-power measuring mechanism in which a measurement index of slit light or the like is projected onto the fundus of the eye to be examined, and the refractive power of the eye is obtained by detecting the index image reflected from the fundus, there is a type in which a index (Placido ring or the like) for measuring the corneal shape is projected with red to infrared light so as to avoid the effect of the miosis of the eye to be measured on the measurement of the refractive power. However, since the red to infrared light is reflected well by the iris, it is even more difficult to discern the change of luminance in the image of the measurement index in the vicinity of the boundary between the pupil and the iris. Hence, it is very difficult to detect the edge of the index image.
The object of the invention is to provide a corneal-shape measuring apparatus which is capable of suppressing the effect due to the light reflected from the iris and of measuring the corneal shape with high accuracy.
To overcome the above-described problems, the invention is characterized by having the following features:
(1) A corneal shape measuring apparatus for measuring a corneal shape of an eye to be examined, the apparatus comprising:
index projecting means having a first projecting optical system for projecting a corneal shape measuring index onto a cornea of the eye;
index detecting means having a first imaging optical system for obtaining an image of an anterior eye segment including an image of the measuring index formed on the cornea;
arithmetic means for obtaining the corneal shape based on the obtained image of the measuring index; and
input means for inputting, to the arithmetic means, information on a boundary position between a pupil and an iris of the eye,
wherein the arithmetic means corrects information on the image of the measuring index based on the information on the boundary position thus inputted, and obtains the corneal shape based on the thus corrected information on the image of the measuring index.
(2) The apparatus of (1), further comprising:
diaphanoscopic image obtaining means having an illuminating optical system for projecting a light onto a fundus of the eye, and illuminating the anterior eye segment with the light reflected from the fundus, and a second imaging optical system for obtaining a diaphanoscopic image of the anterior eye segment; and
boundary position detecting means for detecting the boundary position between the pupil and the iris based on the diaphanoscopic image thus obtained,
wherein the input means inputs information on the thus detected boundary position to the arithmetic means.
(3) The apparatus of (2), wherein the second imaging optical system is used commonly as the first imaging optical system.
(4) The apparatus of (2), further comprising:
occular refractive power measuring means having a second projecting optical system for projecting a light onto the fundus of the eye, and light receiving optical system for receiving the light reflected from the fundus of the eye,
wherein the illuminating optical system is used commonly as the second projecting optical system.
(5) The apparatus of (1), wherein the arithmetic means divides luminance information on the image of the measuring index into a pupil region and an iris region based on the inputted boundary position information, obtains a luminance difference between the pupil region and the iris region, remove reflected light component of the iris region based on the thus obtained luminance difference to correct the luminance information on the image of the measuring index, and obtains the corneal shape based on the thus corrected luminance information.
(6) The apparatus of (1), further comprising:
displaying means for displaying the image of the anterior eye segment thus obtained,
wherein the input means inputs the boundary position between the pupil and the iris based on a display by the displaying means.
(7) The apparatus of (1), wherein the index projecting means includes means for projecting, as the measuring index, a ring pattern index onto the cornea, and the arithmetic means detects an edge position of the obtained ring pattern index, and obtains a corneal curvature based on the detected edge position.
(8) The apparatus of (7), wherein the first projecting optical system provided in the index projecting means includes:
a Placid plate in which light transmitting portions and light shielding portions are alternately arranged substantially concentrically; and
a plurality of light sources for illuminating the Placid plate.
(9) The apparatus of (8), wherein the light sources emits a light whose wavelength falls within red to infrared region.
(10) A corneal shape measuring apparatus for measuring a corneal shape of an eye to be examined, the apparatus comprising:
image input means for inputting an image of an anterior eye segment including a corneal shape measuring index image formed on a cornea;
arithmetic means for obtaining the corneal shape based on the inputted measuring index image;
boundary position input means for inputting, to the arithmetic means, information on a boundary position between a pupil and an iris of the eye,
wherein the arithmetic means corrects information on the measuring index image based on the inputted information on the boundary position, and obtains the corneal shape based on the corrected information on the measuring index image.
(11) The apparatus of (10), further comprising:
diaphanoscopic image obtaining means having an illuminating optical system for projecting a light onto a fundus of the eye, and illuminating the anterior eye segment with the light reflected from the fundus, and an imaging optical system for obtaining a diaphanoscopic image of the anterior eye segment; and
boundary position detecting means for detecting the boundary position between the pupil and the iris based on the diaphanoscopic image thus obtained,
wherein the boundary position input means inputs information on the thus detected boundary position to the arithmetic means.
(12) The apparatus of (11), further comprising:
occular refractive power measuring means having a projecting optical system for projecting a light onto the fundus of the eye, and a light receiving optical system for receiving the light reflected from the fundus of the eye,
wherein the illuminating optical system is used commonly as the projecting optical system.
(13) The apparatus of (10), wherein the arithmetic means divides luminance information on the measuring index image into a pupil region and an iris region based on the inputted boundary position information, obtains a luminance difference between the pupil region and the iris region, remove reflected light component of the iris region based on the thus obtained luminance difference to correct the luminance information on the measuring index image, and obtains the corneal shape based on the thus corrected luminance information.
(14) The apparatus of (10), further comprising:
displaying means for displaying the obtained image of the anterior eye segment,
wherein the boundary position input means inputs the boundary position between the pupil and iris based on a display by the displaying means.
(15) The apparatus of (10), wherein the image input means inputs the image of the anterior eye segment in which an image of a ring pattern index is formed as the measuring index on the cornea, and arithmetic means detects an edge position of the inputted image of the ring pattern index, and obtains a corneal curvature based on the detected edge position.
The present disclosure relates to the subject matter contained in Japanese patent application No. Hei. 11-157265 (filed on Jun. 4, 1999), which is expressly incorporated herein by reference in its entirety.